Newsletters: Fix warnings for non connected authors.

[lezama]

Fixes #39911

Proposed changes:

• Address warnings encountered by non-connected authors in the newsletters feature of the Jetpack plugin.
• These shouldn't show up:

After:

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Create an Author level user
• Enable the Newsletter module
• Create a draft post
• Click on Publish
• Confirm warnings don't show up

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the fix/newsletter-menu-for-authors branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack fix/newsletter-menu-for-authors
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

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[jeherve]

I wonder if we should do more, while we're touching this.

• I don't think that button should be displayed at all when the user is not connected:

• I still see a membership status request returning a 404 (maybe from getNewsletterTierProducts) when the user is not connected. Can we not do any request when the user is not connected?